mersenneforum.org Sierpinski/Riesel Base 5: Post Primes Here
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 2005-06-21, 11:06 #67 axn     Jun 2003 14EF16 Posts 136588*5^22917-1 is prime!
 2005-06-22, 03:43 #68 axn     Jun 2003 10100111011112 Posts 43156*5^44135-1 is prime!
 2005-06-23, 03:35 #69 axn     Jun 2003 23×233 Posts 294698*5^47110-1 is prime!
 2005-07-18, 16:55 #70 jaat     Jul 2005 2·32 Posts Another one bites the dust Prime 9164*5^40892-1 Is there some other way to check these are primes. As the test has some chance of being wrong.(Am i right?) 8494 and 38348 completed upto 50k without any luck. Btw, Is there some statistics/guesses as to how many will fall till say 50k? I got 2/4. jaat
2005-07-18, 17:54   #71
rogue

"Mark"
Apr 2003
Between here and the

19·347 Posts

Quote:
 Originally Posted by jaat Another one bites the dust Prime 9164*5^40892-1 Is there some other way to check these are primes. As the test has some chance of being wrong.(Am i right?)
Yes, you can use WinPFGW to do a primality test with the -tp switch (or -tm for a +1 number). No, unless there is a bug in the software or if there were a hardware problem, the number is prime.

2005-07-19, 09:40   #72
geoff

Mar 2003
New Zealand

13·89 Posts

Quote:
 Originally Posted by jaat Btw, Is there some statistics/guesses as to how many will fall till say 50k? I got 2/4.
From the Sierpinski data so far I would guess that a little more than 1 in 3 candidates will be eliminated by finding a prime with an exponent between 20,000 and 50,000. The 4 candidates you worked on were of average combined weight, so I would say you did just a little better than average to eliminate 2.

(I moved the last two messages from the reservations thread)

 2005-07-19, 20:21 #73 jaat     Jul 2005 2·32 Posts Thanks to both Rogue and geoff for answering the queries. I checked both the numbers with the WinPFGW and they are prime. It is also nice to know that one can knock a very large fraction of them very quickly. I'll get back to them soon. jaat
 2005-08-14, 05:31 #74 geoff     Mar 2003 New Zealand 48516 Posts I wondered if any of the primes we find could be one of a pair of twin primes of the form k*5^n+/-1. Since in any three consecutive integers one must be divisible by 3, for both k*5^n+1 and k*5^n-1 to be prime, k must be divisible by 3. It turns out that this is possible for just one of the k we are currently testing, the Riesel candidate k=151026. Of the primes already found, the two largest twin primes of this form were 110538*5^139+/-1 and 136674*5^172+/-1.
 2005-09-15, 07:29 #75 OmbooHankvald     May 2005 Copenhagen, Denmark 172 Posts Hey all. I was wondering: Is this project still "alive"? There is not a lot going on in the forum and only geoff has found primes in the last month, so I started to wonder how many people (or GHz) are working on this problem? I think I'll get back here when I'm finished with my 2721...
 2005-09-17, 15:16 #76 geoff     Mar 2003 New Zealand 100100001012 Posts I have a part time 2.66GHz P4 that I split between this project and PSP, it usually does 8-10 hours per week. It is quiet at the moment, but that is OK, there is no rush :-)
 2005-10-11, 07:47 #77 axn     Jun 2003 10100111011112 Posts 99356*5^34994-1 is prime!

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